Electrical stimulation is an effective therapy for a variety of conditions and diseases that adversely affect patient health. For example, electrical stimulation has been effective in alleviating chronic pain, movement disorders, gastrointestinal disorders, and pelvic floor disorders. Spinal cord stimulation systems have been found to provide relief for chronic pain. Deep brain stimulation can be effective in treatment of movement disorders such as Parkinson's disease, as well as other neurological disorders such as epilepsy. Stimulation of the gastrointestinal tract can be effective in alleviating gastroparesis and obesity. Stimulation of the pelvic floor can be effective in alleviating urinary incontinence, fecal incontinence, pelvic pain, and sexual dysfunction.
Typically, electrical stimulation is delivered by an implantable pulse generator that is chronically implanted within the patient. One or more implantable leads extending from the implantable pulse generator carry electrodes for delivery of stimulation energy to a target tissue or nerve site. A lead typically carries a set of ring electrodes. Each ring electrode extends about the circumference of the lead, and is positioned at a respective axial position along the length of the lead. In operation, different combinations of electrodes, either on a single lead or among multiple leads, can be selected for delivery of electrical stimulation energy to the patient.
The particular combinations and polarities of the electrodes may define the shape or direction of a stimulation pattern. Different combinations of electrodes may be tested to identify a configuration that provides suitable efficacy for the patient. Efficacy may be evaluated in terms of the degree of relief of symptoms of a targeted disorder, as well as severity of any side effects. The availability of multiple electrodes in the vicinity of a stimulation site increases the likelihood that an efficacious electrode combination will be identified. In addition, the electrode combination may be changed over the course of therapy to restore efficacy or explore other effective combinations. In some cases, selection of alternate electrode combinations may be necessary due to lead migration within the patient, progression of symptoms or an underlying ailment, or late onset of side effects.